/*
 * Copyright 2017 Huawei Technologies Co., Ltd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.servicecomb.core.handler.impl;

import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;

import io.servicecomb.core.Endpoint;
import io.servicecomb.core.Invocation;
import io.servicecomb.core.endpoint.EndpointsCache;
import io.servicecomb.core.exception.ExceptionUtils;
import io.servicecomb.swagger.invocation.AsyncResponse;

/**
 * 内置轮询lb，方便demo之类的场景，不必去依赖lb包
 */
public class SimpleLoadBalanceHandler extends AbstractHandler {
    private AtomicInteger index = new AtomicInteger();

    // key为transportName
    private volatile Map<String, EndpointsCache> endpointsCacheMap = new ConcurrentHashMap<>();

    @Override
    public void handle(Invocation invocation, AsyncResponse asyncResp) throws Exception {
        // 调用者未指定transport时，这里得到的是""，也直接使用，不必特殊处理
        String transportName = invocation.getConfigTransportName();

        EndpointsCache endpointsCache = endpointsCacheMap.get(transportName);
        if (endpointsCache == null) {
            synchronized (this) {
                endpointsCache = endpointsCacheMap.get(invocation.getConfigTransportName());
                if (endpointsCache == null) {
                    endpointsCache = new EndpointsCache(invocation.getAppId(), invocation.getMicroserviceName(),
                            invocation.getMicroserviceVersionRule(), transportName);
                    endpointsCacheMap.put(transportName, endpointsCache);
                }
            }
        }
        List<Endpoint> endpoints = endpointsCache.getLatestEndpoints();

        if (endpoints == null || endpoints.isEmpty()) {
            asyncResp.consumerFail(ExceptionUtils.lbAddressNotFound(invocation.getMicroserviceName(),
                    invocation.getMicroserviceVersionRule(),
                    transportName));
            return;
        }

        int idx = Math.abs(index.getAndIncrement());
        idx = idx % endpoints.size();
        Endpoint endpoint = endpoints.get(idx);

        invocation.setEndpoint(endpoint);

        invocation.next(asyncResp);
    }

}
